Dammed if you do and dammed if you don't!
If you pass the OM/FAF/1000' point with RVR < 550m you have broken the approach ban despite being meeting all the requirements for a catI landing. Fail.
So if you do land, expect a call from 'The Authority' and if you divert expect a call from Dir of Flt Ops. Either way you're going to be short on the tea and biscuits front. Do like the idea of the proactive ATCO realising the paradox of the situation and declaring the RVR equipment U/S and thus allowing pilots to continue to DA. However from a flight safety perspective this approach whilst legally acceptable does require a cloud base to be of sufficient height to allow reasonable time to assess the lighting requirements. As such it should be treated with caution.